1. Field of the Invention
The present invention relates to the field of compression release engine braking.
2. Description of the Background Art
Compression release engine braking, or simply engine braking, is an engine operating mode wherein the engine is reconfigured during operation to provide a braking effect to a vehicle by essentially turning the engine into a compressor. This may be desirable or necessary when regular wheel brakes are inadequate to provide complete braking. An example is a need for powerful and prolonged braking operations by heavily loaded trucks on steep grades, such as on mountain roads. Engine braking finds particular applicability on large vehicles having high wheel weights and correspondingly high momentum, and where conventional wheel brakes may fade or fail under high loading conditions or under prolonged use.
Engine brakes commonly operate by shutting the fuel off to the engine and simultaneously opening one or more exhaust valves for the engine cylinders near top dead center (xe2x80x9cTDCxe2x80x9d) of the cylinders"" compression strokes. This in effect causes the engine to do work in compressing the engine intake gases without allowing it to recover the energy of compression during the expansion strokes of the cylinders. Thus, energy is dissipated by the engine and the vehicle is thereby slowed without having to use standard wheel brakes.
Turbocharged engines are also well known in the art. A standard turbocharger uses the exhaust gases from the engine to spin a turbine. The mechanical energy of the turbine is then used advantageously to compress the intake air of the engine. Furthermore, an intercooler, essentially an air-to-air heat exchanger, is often used concurrently to cool the compressed intake air from the turbocharger so that it does not enter the engine at too high a temperature.
Rowells, U.S. Pat. No. 5,634,447, discloses an approach to engine braking wherein fuel is injected into a turbocharged non-intercooled engine during engine braking for increased braking power. Rowells injects a small quantity of fuel into the cylinders of the engine well in advance of top dead center on the compression stroke. The small amount of fuel combusts, thus raising cylinder pressure during compression and increasing energy to the turbocharger, inherently increasing braking power. However, when the engine utilizes an intercooler (air-to-air) which greatly reduces the intake air temperature into the engine, combustion engines experience problems burning the fuel injected during engine braking due to the cool temperature of the intake combustion air, especially in colder climates. At middle to lower engine speeds, the fuel is even harder to ignite. Thus, where engine braking is needed the most, e.g., in class 8 heavy duty trucks which are all intercooled (air-to-air), the positive effect of the approach disclosed in Rowells is negated.
Kulig et al., U.S. Pat. No. 5,385,019, discloses an approach to increasing the engine braking power and efficiency of an internal combustion engine equipped with a turbocharger and intercooler assembly. Kulig increases the mass flow of intake air to the engine by bypassing the intercooler during operation of the engine brake. The Kulig patent explains that this is done in order to provide higher pressure air to the intake manifold of the engine, thus requiring more work from the engine to compress the air. As engine speed decreases, however, the turbocharger compresses the engine intake air less and less. The engine braking approach disclosed in Kulig becomes less effective at lower engine speeds.
Therefore, there remains a need in the art for improvements in engine braking systems.
The method of the present invention includes bypassing intake air around the intercooler from the turbocharger while simultaneously injecting a minimum amount or greater of fuel per stroke into an engine cylinder during engine brake operation. The minimum amount of fuel is determined such that it is the smallest amount of fuel which will fully combust when the engine is operating at a given speed.
The apparatus of the present invention is an improvement upon standard internal combustion engines equipped with a turbocharger, an intercooler, and a compression release brake. The compression release brake comprises a compression release brake controller, a fuel injector assembly, and an intercooler bypass assembly. The apparatus operates such that during engine braking, a small amount of fuel is injected into the cylinders during the compression stroke, and engine intake air is bypassed around the intercooler from the turbocharger and directly into the engine.
Engine braking done using a simultaneous minimum fuel injection (or greater) and intercooler bypass causes a synergistic increase in engine braking power and efficiency throughout the speed range. Increased engine intake air temperature and pressure resulting from the intercooler bypass during engine braking causes a minimum amount of fuel injected into the engine cylinders to be more completely combusted by the compression stroke than if no bypass had been done. This combustion alone dissipates more energy during braking, but also results in higher temperature and pressure exhaust gases. These higher energy exhaust gases in turn provide more power to the turbocharger which then compresses the intake air more, thus compounding the initial bypass effect. Furthermore, the amount of fuel which must be injected to obtain a given braking power during engine braking with intercooler bypass is necessarily less than without bypass. Thus, overall fuel economy is improved.
The above and other features and advantages of the present invention will be further understood from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings.